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Open Roads Forum  >  Tech Issues

 > 12V question--simple, please!

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mockturtle

WA

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Posted: 08/11/12 07:58pm Link  |  Print  |  Notify Moderator

I know zilch about these things so please keep it as basic as possible. I bought a 50W room air filter for my bedroom and would like to use it in the MH, as well, even when dry camping using my little 100W inverter. Question: How many amp-hours will it use to run it, say, for seven hours at night? Thank you.


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pianotuna

Regina, SK, Canada

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Posted: 08/11/12 08:15pm Link  |  Print  |  Notify Moderator

Hi mockturle,

Divide the wattage by 10. It will "burn through" 5 amps per hour. 7 x 5 = 35 amp-hours.


Regards, Don
Full Time in a Kustom Koach Class C 28'5", 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, Magnum 3000 watt PSW inverter.

MrWizard

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Posted: 08/11/12 08:42pm Link  |  Print  |  Notify Moderator

Don is right, divide watts by ten and multiply by the number of hrs is the quick way to get a close number

with an inverter efficency loss of 12% you will use 392watt hrs
32>35 AmpHrs depending on state of batteries before and after


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mockturtle

WA

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Posted: 08/11/12 08:44pm Link  |  Print  |  Notify Moderator

Great! Thanks, guys!

wa8yxm

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Posted: 08/12/12 06:22pm Link  |  Print  |  Notify Moderator

Some years ago I did a whole bunch of math, it included the average effiency of an inverter, and a bunch of other stuff....

Found out that using the "Divide watts by 10" method Don suggested.

Works great

50 watts / 10 volts = 5 amps times 7 hours = 35 amp= hours Times 2 to be safe = one group 24 battery or larger. (G-24 if it is the ONLY thing running on batterie.

The rule is you can use 1/2 of a deep cycle battery, only about 1/4 of a marine/deep cycle and still be safe.

A pair of GC-2 Golf car batteries in series. that is 230 amp h ours, 115 usable and a very good choice for your installation


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kneal44

EAST CENTRAL TEXAS

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Posted: 08/12/12 06:40am Link  |  Print  |  Notify Moderator

at walmart i got a 12 volt fan i use, and works well it draws 2 amps and over nite thats 20 amp hours.

its not noisy and cools you off for sleeping.
fan cost $10 now.


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pianotuna

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Posted: 08/13/12 06:53am Link  |  Print  |  Notify Moderator

Hi Almot,

The divide by ten does cover inverter losses, so there is no need to "up" the amp-hours used. (Is that more clear W8?)

* This post was edited 08/13/12 03:49pm by pianotuna *

wa8yxm

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Posted: 08/13/12 01:13pm Link  |  Print  |  Notify Moderator

Not sure if you are making a statement or asking a question Piano fish, but if it's a question the answer is yes. It does, and a slight bit more. (just to play safe) plus the O/P said "keep it easy" and not much is easier than divide by 10.

Almot

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Posted: 08/12/12 11:59pm Link  |  Print  |  Notify Moderator

Yep. What the last poster said. You can't/shouldn't drain the battery to less than 50% of full capacity. So if it is fully charged before you use it (fully means 100%, not 90%, stupid green light on panel is not too accurate), and air filter is the ONLY thing that this battery is used for, then it draws 40 Ah in 7 hours (inverter needs some juice for itself) and you need 80 Ah battery. Better make it 90 Ah. Again, this is if there is NOTHING else running off this battery, just air filter.

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